I’m almost recovered from my recent obsession with “end-of-the-world” scenarios. I’m not certain what drove me down this route. Maybe it was discovering my (now-repaired) aortic aneurysm (which could have killed me three years ago). Or, I could blame it on the 2004 Red Sox World Series victory. I always thought the world would end before the BoSox overcame the Curse of the Bambino. In any event, I wasted too much time investigating the various scenarios proposed for Earth’s final doomsday — the moment when our planet (at least all of its inhabitants) is finally obliterated. Maybe I just needed an anti-anxiety pill or a stronger martini!

Evaluating the end of the world is doubly challenging when you begin the process, as I did, stretched out on a sunny condo balcony overlooking the Pacific Coast of Kauai. The biggest problem offshore surfers have is which perfect wave to ride. If Earth’s last day is coming, can I please await it on the Hawaiian Islands?

Hollywood, TV and the print media have flooded an apparently catastrophe-starved public with apocalyptic scenarios. I brought a personal catastrophe library to Hawaii, relieved that TSA agents didn’t scrutinize my suitcase contents. If you’re “terminally obsessed,” the following should be on your “must have” list for an end-of-summer or gloomy winter read-in: A Guide to the End of the World and Surviving Armageddon, both by Bill McGuire; Catastrophes And Lesser Calamities by Tony Hallam; The Long Emergency by James Howard Kuntstler; The Life and Death of Planet Earth by Peter D. Ward and Donald Brownlee; Perilous Planet Earth by Trevor Palmer; and Extinction by Douglas Erwin.

Reading these books is demoralizing. Those with especially weak psyches should instead check out the light-hearted and humorous Web site www.exitmundi.nl. (Exit mundi roughly means “the world leaves.”) Like most of the books, the site categorizes Earth’s final curtain in various ways — for example, immediacy (imminent, the next few decades, next century, thousands of years and even millions to billions of years in the future). Apocalyptic scenarios can also be organized on the basis of their origin: space (meteorite impacts, stellar explosions and invading aliens); terrestrial (freezing of the core, catastrophic tsunamis, earthquakes and volcanoes); human activity (technology running amok, global warming, nuclear war and uncontrolled terrorist-generated pandemics); and the end of the world as envisioned by different religions.

After identifying Earth-ending cataclysms, I began to rank them in terms of likelihood and to evaluate the means by which they might be avoided. A new book by Richard A. Posner, Catastrophe: Risk and Response (2004) short-circuited this effort. Posner, an incredibly bright scholar, is a judge of the U.S. Court of Appeals for the Seventh Circuit and a lecturer at the University of Chicago Law School. His approach — logical and straightforward — contrasts with my panic.

Posner argues that major catastrophic risks should be first assessed by gauging their statistical likelihood, the purely physical consequences of each, and the possible measures by which the risks or magnitude of the consequences might be reduced. In a nutshell, his approach is basically cost-benefit analysis, granted with incredibly high potential costs and immeasurable benefits — it’s our world or nothing! He discusses in detail several specific potentially world-ending scenarios including global warming, a runaway atomic accelerator, and impacting asteroids and comets.

Consider the collision of extraterrestrial bodies with Earth. Posner argues that it is foolish to expect any government to develop and deploy surveillance and defense systems without first estimating the cost of such systems, the likelihood of actual collisions, the level of destruction such collisions produce and the “benefits” of doing nothing. He comes down solidly in favor of making a greater effort to detect and prevent asteroid and comet collisions.

He also favors doing more to arrest global warming, but is decidedly hesitant about investing unlimited time and energy to prevent intentional human-caused catastrophes, such as bioterrorism and nuclear explosions unleashed by small groups. He argues that no known existing germ is easily spread globally and is universally lethal enough to destroy all humans. He concedes that while the expected costs of a terrorist bomb or bombs are high, these effects of such attacks are subcatastrophic rather than “globally terminal.”

Some threats to Earth’s existence can and probably should be ignored: those with either an infinitesimally small likelihood and those without conceivable means for detection, prevention or mitigation. Earth could suddenly be swallowed by a black hole. A catastrophic stellar explosion might obliterate life. The sun is certain to eventually die. We are powerless to prevent such events and “moving away” is not a realistic possibility. Instead, we must concentrate on averting phenomena that are detectable, quasi-probable, avoidable and can be mitigated.

So, where do we go from here? A few preliminary steps are in order. Governments of technologically advanced nations (the only ones with the capacity to launch a first line of defense) should coordinate the first steps in meeting potential threats. They will do so only if pressured by an educated public enlightened by the scientific community. Scientists must brush up on their understanding of statistics and cost-effective risk assessment, and improve their ability to communicate with the public. Scientific literacy is already shaky, and in a world awash with rash, unsound predictions, citizens hesitate to consider risks that are both statistically very rare (low probability over short time spans) and with which they have no practical experience.

In the meantime, I am much more upbeat about our long-range prospects, and I am again buying green bananas. For now, I’m redirecting my misplaced attention toward unresolved tangible and urgent issues: the energy crisis, inadequate global healthcare, and the political and religious differences that increasingly drive the disparate citizens of this planet apart. Facing and solving these problems will stave off the apocalypse for now — I hope.

Schwab is a professor of geology at Washington and Lee University in Lexington, Va. E-mail: schwabf@wlu.edu.